The only near useless spell I've seen named here is Goblin Punch. Berserk is great if you know how to use it properly. Float is useful if you want to beat the Brothers in Final Fantasy VIII, avoid Hildegigas earthquake in IX, and to avoid traps in XII. Vanish makes you immune to physical attacks and makes enemies 100% to any spell.

For me Goblin Punch and Jewel are the only ones I find bordering on useless territory.